Tetrahedral junction waveguide switches are used in many millimeter wave applications. One such switch is disclosed in U.S. Pat. No. 4,843,357 entitled "Tetrahedral Junction Waveguide Switch" issuing to Stern et al on Jun. 27, 1989, which is herein incorporated by reference. Therein disclosed is a waveguide switch employing two lengths of waveguides for transmitting electromagnetic energy joined by a tapered rod of ferrite material. The two waveguides each have a major transverse axis. The major transverse axes of each of the two waveguides are made orthogonal. At their junction, the ferrite rod is positioned thereat. The rod's longitudinal axis coincides with the longitudinal axis of the two joined waveguides. A longitudinal magnetic field is applied to the ferrite rod by a permanent magnet structure. As a result of the well known Reggia-Spencer effect, when the ferrite rod is subjected to a unidirectional magnetic field along its longitudinal axis, the permeability of the rod is changed permitting electromagnetic wave energy to pass through the aperture adjoining the two waveguides. Therefore, the permanent magnet provides a magnetic field that biases the switch permitting electromagnetic wave energy or a signal to pass through the waveguide junction.
In some applications, it is desirable to prevent or cut off electromagnetic wave energy from being transmitted through the waveguide. For example, this is commonly done to protect a radar receiver during the duration of the radar transmitting pulse. However, when the radar echo is received, the waveguide must be in a state to transmit the substantial reduced electromagnetic wave energy echo signal. In order to place the waveguide switch in a cut off or non-transmission state, the longitudinal magnetic field must be removed from the ferrite rod. This is accomplished by a helical coil circumscribing the waveguide junction and ferrite rod. Therefore, when the waveguide switch is to be placed in a non-transmission state or mode, the appropriate current is applied to the helical coil resulting in another longitudinal magnetic field opposing that of the longitudinal magnetic field created by the permanent magnet. Therefore, no net longitudinal magnetic field is applied to the ferrite rod resulting in the prevention of electromagnetic wave energy from being transmitted through the waveguide switch.
While the prior art waveguide switches have performed adequately in many applications, there remain several disadvantages. The permanent magnetic structures and the required helical coil results in a relatively heavy and bulky or large waveguide switch. Additionally, the necessity to use a generated magnetic field to oppose the magnetic field of the permanent magnet results, over a period of time, in the compromising of the performance of the permanent magnet structure. Additionally, the necessity to balance the two opposing magnetic fields to provide a non-transmission state of the waveguide results in additional controls being required. This is especially true as the properties of the permanent magnetic material and thereby resulting magnetic field may change in time. With many of the applications of a waveguide switch being used in aircraft, there is a continuing need to reduce the size, weight, and energy requirements of a waveguide switch.